1. Field of the Invention
The present invention relates to a low pass filter of a radio transmitter and, in particular, a low pass filter capable of attenuating harmonic and spurious frequency.
2. Description of the Related Art
As radio paging subscribers are presently increasing, a paging system for transmitting radio paging data is also extended in correspondence with the above increase. While the paging system provides paging data signals of good quality for subscribers, a paging transmitter (hereinafter, referred to as a transmitter) converts the paging data signal into a radio frequency RF signal and transmits the converted signal. At this time, an electronic feature of the transmitter determines quality of radio paging service thereof.
Therefore, generation of harmonic and spurious frequency in a radio paging frequency band can deteriorate the quality of the paging service of the transmitter. Generally, in order to suppress the generation of the harmonic and the spurious frequency, the transmitter uses a number of filters between a signal source and a termination outputting signal. For instance, a low pass filter using a general capacitor can be used in order to suppress the harmonic generation in the transmitter. However, a common low pass filter can be embodied as an elliptic low pass type filter capable of diminishing cost by reducing the number of components of the above low pass filter because of having a limit in a space where the components are mounted.
In this case, even if the above elliptic low pass type filter can diminish cost by reducing the number of components thereof, it has a reduced capability of suppressing and attenuating the generation of the fifth harmonic or more.